The present invention relates to a method of hermetically sealing electronic packages such as are used in radar systems. The electronic packages are typically box-like packages with r.f. connectors sealed through the package or module walls. Electronic components are mounted within the package which is hermetically sealed by soldering in place top and bottom cover members. Such prior art solder sealing requires heating the entire package, which is typically aluiminum, to a temperature which may adversely affect the electronic components within the package. The soldering of the cover to the package is carried out by local heating using a propane torch or soldering iron.
It is not unusual for such electronic packages to be reopened or delidded during assembly and testing, for adjustment or replacement of electronic components. If such solder sealed packages must be dissassembled by removing the soldered cover or lid, the package must be reheated to melt the solder, and the solder removed from the seal area to prevent entry of the solder into the package. Such delidding of solder covers is a time consuming and tedious operation. Furthermore, for aluminum packages a nickel/tin layer must be plated on the solder seal area to permit adherence of the solder to the aluminum package.
The electronic package or modules operate in the UHF or microwave region of the electromagnetic spectrum. In most designs it is necessary to provide electrical isolation between various components to prevent electrical coupling and possible instabilities. This is accomplished by compartmentalizing the chassis or package, and attaching a flexible conductive seal to the underside of the cover in the areas of the compartment walls. The cover is then tightly screwed onto the module to compress the seal and provide the required isolation. The present method for sealing the screw holes in the cover is by soldering discs over these holes. Electronic components are disposed with the various compartments of the package or module.
These modules require the attachment of hermetically sealed r.f. and power connectors which are connected to the electronic components within the package. The current method is to nickel/tin plate the connectors in the areas to be soldered and then solder them to the nickel/tin plated chassis using a high temperature solder (such as tin/silver which melts at 221.degree. C.) prior to assembly of the components. After assembly, the cover may be soldered in place with the lower temperature solder without adversely affecting the connector solder joint. However, heating the connectors to such elevated temperatures can cause failures at the glass to metal seals.
The prior art solder sealing process has serious disadvantages including requiring a high degree of operator skill with accurate control of soldering parameters required. The heating requirements during normal sealing as well as during delidding subject the electronic components to possible thermal damage, and repair of leaks requires further thermal treatment.